1. Field of the Invention
This invention relates to means for withdrawing gaseous effluents preferentially to liquid effluents in an ebullated bed process. The invention also related to improved control of an ebullated bed process. The control relates to removing gas preferentially to removing liquid from an ebullated bed reactor.
2. Description of Other Relevant Methods in the Field
The ebullated bed process comprises the passing of concurrently flowing streams of liquids or slurries of liquids and solids and gas through a vertically cylindrical vessel containing catalyst. The catalyst is placed in random motion in the liquid and has a gross volume dispersed through the liquid medium greater than the volume of the mass when stationary. This technology has found commercial application in the upgrading of heavy liquid hydrocarbons or converting coal to synthetic oils.
The process is generally described in E. S. Johanson U.S. Pat. No. Re 25,770 incorporated herein by reference. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are forced into random motion as the liquid and gas pass upwardly through the bed. The catalyst bed motion is controlled by a recycle liquid flow so that at steady state, the bulk of the catalyst does not rise above a definable level in the reactor. Vapors along with the liquid which is being hydrogenated pass through that upper level of catalyst particles into a substantially catalyst free zone and are removed at the upper portion of the reactor.
In an ebullated bed process the substantial amounts of hydrogen gas and light hydrocarbon vapors present rise through the reaction zone into the catalyst free zone. Liquid is both recycled to the bottom of the reactor and removed from the reactor as product from this catalyst free zone. Vapor is separated from the liquid recycle stream before being passed through the recycle conduit to the recycle pump suction. The recycle pump (ebullation pump) maintains the expansion (ebullation) and random motion of catalyst particles at a constant and stable level. Gases or vapors present in the recycled liquid materially decrease the capacity of the recycle pump as well as reduce the liquid residence time in the reactor and limit hydrogen partial pressure.
Reactors employed in a catalytic hydrogenation process with an ebullated bed of catalyst particles are designed with a central vertical recycle conduit which serves as the downcomer for recycling liquid from the catalyst free zone above the ebullated catalyst bed to the suction of a recycle pump to recirculate the liquid through the catalytic reaction zone. The recycling of liquid from the upper portion of the reactor serves to ebullate the catalyst bed, maintain temperature uniformity through the reactor and stabilize the catalyst bed.
M. C. CherVenak et al. U.S. Pat. No. 4,221,653. describes an apparatus for separating vapor from liquid in an ebullated bed process. The apparatus comprises a frusto-conical cup in which are inserted a plurality of riser conduits. The conduits are positioned in two concentric circles within the cup. The generic term for the recycle gas-liquid separator apparatus in an ebullating bed process is a recycle cup. The recycle cup of the Chervenak et al. patent and those like it with a plurality of riser conduits are referred to as a tubular recycle cup.
It is a critical feature of the recycle cup that the upflowing liquid-gas mixture rising from the reaction zone passes through the riser conduits of the separation apparatus and that lower ends of all conduits are below the reactor liquid level.
After passage through the recycle cup, the gas portion rises to the top of the reactor. Part of the liquid portion is returned through a downcomer conduit and recycled to the reaction zone. The remaining liquid portion is withdrawn from the reactor as liquid product. The returned liquid portion passes through the recycle conduit to a recycle pump, then passes through a liquid-gas distribution means, together with fresh liquid and hydrogen feed to maintain uniform upward fluid flow through the ebullated catalyst bed. Liquid and vapor are withdrawn through a conduit extending into the reactor adjacent the separator apparatus.
A. G. Comolli U.S. Pat. No. 4,151,073 and P. H. Kydd U. S. Pat. No. 4,354,852 recognize the advantages of effecting the recycle liquid-vapor separation in an ebullated bed process by feeding the fluid tangentially to a cylindrical separator. By this method, the hot fluid is fed to the cylindrical separator at conditions to prevent carbonaceous particulate material from depositing on the interior surface of the separator. These conditions include tangential injection of feed to the separator, fluid temperature of 550.degree. F. to 900.degree. F. and a separator length/diameter ratio of 20/1 to 50/1. The Kydd patent additionally teaches that a liquid vortex in the cylindrical separator reduces coke deposition.
J. I. Harper et al. U.S. Pat. No. 2,706,167 teaches an ebullated bed process wherein in the drawing, liquid and vapor are withdrawn from the reactor separately.
R. P. Van Driessen U.S. Pat. No. 3,188,286 teaches an apparatus for carrying out an ebullated bed process. The apparatus comprises a treating vessel; means for introducing liquid, gas and catalyst into the vessel; a withdrawal conduit extending into the upper portion of the vessel having a vertically extending screen portion positioned to maintain an upper level in the vessel and to permit gas and liquid to separately enter the conduit for withdrawal from the vessel.
C. L. Weber et al. U.S. Pat. No. 3,677,716; 3,622,265 and 3,819,331 teach an apparatus for gas-liquid-solid phase separation for use in an ebullated bed process. The apparatus comprises gas disengaging means, a solid setting chamber enclosed such that liquids and solids within the chamber are substantially out of contact with the turbulent zone and means to withdraw gas.
M. C. Chervenak et al. U.S. Pat. No. 3,539,499 teaches an ebullated bed process wherein vertical baffles above the dense catalyst phase are used to reduce entrainment of undissolved hydrogen and entrained gases in the liquid product.
L. M. Lehman et al. U.S. Pat. No. 3,549,517 teaches an ebullated bed process wherein in the drawing, liquid and vapor are withdrawn from the reactor separately.
C. E. Adams et al. U.S. Pat. No. 3,668,116 teach an ebullated bed process wherein in the drawing, a liquid cyclone is used for separation.
A. A. Gregoli et al.U.S. Pat. No. 3,698,876 teaches an ebullated bed process. In the process a funnel shaped apparatus with vertically mounted vanes is used in the internal liquid recycle conduit for vapor-liquid disengagement.